Re: [PATCH 1/2] x86/cpufeatures: Add the Virtual SPEC_CTRL feature

[Babu Moger]

On 12/7/20 5:22 PM, Jim Mattson wrote:
> On Mon, Dec 7, 2020 at 2:38 PM Babu Moger <babu.moger@xxxxxxx> wrote:
>>
>> Newer AMD processors have a feature to virtualize the use of the SPEC_CTRL
>> MSR. This feature is identified via CPUID 0x8000000A_EDX[20]. When present,
>> the SPEC_CTRL MSR is automatically virtualized and no longer requires
>> hypervisor intervention.
>>
>> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
>> ---
>>  arch/x86/include/asm/cpufeatures.h |    1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index dad350d42ecf..d649ac5ed7c7 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -335,6 +335,7 @@
>>  #define X86_FEATURE_AVIC               (15*32+13) /* Virtual Interrupt Controller */
>>  #define X86_FEATURE_V_VMSAVE_VMLOAD    (15*32+15) /* Virtual VMSAVE VMLOAD */
>>  #define X86_FEATURE_VGIF               (15*32+16) /* Virtual GIF */
>> +#define X86_FEATURE_V_SPEC_CTRL                (15*32+20) /* Virtual SPEC_CTRL */
> 
> Shouldn't this bit be reported by KVM_GET_SUPPORTED_CPUID when it's
> enumerated on the host?

Jim, I am not sure if this needs to be reported by
KVM_GET_SUPPORTED_CPUID. I dont see V_VMSAVE_VMLOAD or VGIF being reported
via KVM_GET_SUPPORTED_CPUID. Do you see the need for that?


>>  /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */
>>  #define X86_FEATURE_AVX512VBMI         (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/
>>